This invention relates to a battery charging apparatus for charging a rechargeable battery.
Rechargeable batteries such as nickel cadmium batteries, nickel hydrogen batteries, etc., which can be used repeatedly, are widely employed as a power source for portable electronic equipment. These rechargeable batteries are charged by attachment to a battery charging apparatus. During charging, rechargeable batteries are subject to self heating and the effects of heat radiated from the power supply and other circuits of the charging apparatus. It is possible for the batteries to be put in an abnormally high temperature state.
If a rechargeable battery is subjected to abnormally high temperature, battery characteristics will be degraded. To avoid abnormally high rechargeable battery temperature, battery temperature is monitored and charging is interrupted when battery temperature exceeds a specified value as disclosed in Japanese Non-examined Patent Publication No. 64-19923 issued on Jan. 24, 1989. In this disclosure, charging is resumed when rechargeable battery temperature again drops below the specified temperature.
However, the purpose of the above technology is to prevent degradation of battery characteristics. Therefore, no consideration is given to rechargeable battery temperature when full charge is reached. Consequently, when a rechargeable battery reaches full charge, it has become hot. When an attempt is made to remove the battery from the charging apparatus, the undesirable impression is made that either the charging apparatus or the rechargeable battery has a problem.
Thus it is an object of the present invention to avoid having the rechargeable battery in a high temperature state when it has reached full charge and is ready to be removed from the charging apparatus.